In the production of printed-circuit boards a thin metal foil is juxtaposed to a board or plate impregnated with a synthetic resin, the two layers subsequently being heated and pressed together. Generally, a plurality of laminations each including at least one base board and at least one metal foil are interleaved with pressure plates prior to a single compression operation.
The foil sections, the base boards and the pressure plates are stacked in a predetermined order at a stacking station which includes a vertically shiftable support table, conveyance devices for depositing the plates and the boards on the table and a tensioning device for stretching each metal-foil section out over an underlying plate or board and subsequently depositing the section thereonto. The conveyance devices and the tensioning device operate in alternating phases of a stacking cycle. The support table is frequently the lower platen of a press.
The resin-impregnated base boards or carrier mats are generally fabricated from glass or paper fibers and a resin such as a phenolic.
Assemblies are known, such as German patent document (Deutsche Patentschrift) DE-PS No. 2,209,691, for forming a stack of fiber boards and heat-treated veneers or foils which are then pressed together to form wall paneling. The conveyance device for depositing the fiber boards on the support table comprises a pair of tongs for gripping opposite ends of each board and bending the same in a downwardly convex curve, whereby a central linear portion of the board makes contact with the underlying surface along a line. The tongs or grippers are then opened or spread apart, whereupon the uplifted lateral portions of the board flap down onto the respective underlying surfaces and engage the same in a center-to-outer-edge wave-type motion which forces air from the space between upper and lower lamination layers. As described in German patent document DE-PS No. 2,209,691, the tongs or grippers of the conveyance device may be provided with actuators.
Stacking assemblies of the above-mentioned type are unsuited for depositing a thin foil onto an underlying plate or lamination layer. Frequently the foil has folds or crimps upon placement and pockets of air are trapped between the foil and the plate. Such folds and air pockets are largely unacceptable in printed-circuit boards.